Although vaccines are available to prevent many types of viral infection, not all viruses are able to be prevented by a vaccine and not all potential victims are able to receive vaccinations even if they are available. For example, the retrovirus human immunodeficiency virus (HIV) causes Acquired Immunodeficiency Syndrome (AIDS), an incurable disease for which there is no vaccine in which the body's immune system breaks down leaving the victim vulnerable to opportunistic infections, e.g., pneumonia, and certain cancers, e.g., Karposi's Sarcoma. Many patients with HIV are co-infected with Hepatitis C Virus (HCV), Hepatitis B (HBV), or other viruses. Although a vaccine is available for certain viruses such as HBV, many at-risk people do not receive or have access to the vaccine. Further, some data indicate that the HBV vaccine is not as effective in people already infected with HIV.
Viral infections, once established, are generally incurable. There are, however, a variety of anti-viral drugs that can prevent viruses from reproducing and ravaging the body's immune system, i.e., that slow the infection and lengthen the subject's life. However, such therapies often only partially effective, and it is unknown how much viral suppression is required to achieve durable virologic, immunologic, and clinical benefits. Anti-viral drugs are often highly toxic and can cause serious side effects, including heart damage, kidney failure, and osteoporosis.
For example, highly active antiretroviral drug therapy (HAART) is a widely used anti-HIV therapy that entails multiple-drug protease inhibitor-containing regimens that can completely suppress viral replication. Hepatic injury is a major concern as a result of antiretroviral therapy (HAART) and has been shown to occur with all classes of antiretroviral therapy. The efficacy of current anti-HIV therapy is further limited by the complexity of regimens, pill burden, and drug-drug interactions. Compliance with the toxic effects of antiretroviral drugs make a lifetime of combination therapy a difficult prospect and many patients cannot tolerate long-term treatment with HAART. Further, poor adherence to combination therapy regimes has led to the emergence of drug-resistant strains of HIV.
There is clearly a need for new anti-viral agents and other novel approaches to treating viral infection.